A zero-dimensional hybrid manganese bromide with long luminescence lifetime, temperature-dependent emissions, and glass transition behavior

Zero-dimensional (0D) hybrid manganese halides have received substantial attention due to their excellent optoelectronic properties. Herein, a 0D hybrid manganese bromide [DMPBA]₂[MnBr₄] (DMPBA⁺ = Dimethylphenylbenzylammonium) was successfully synthesized. In the structure, there are not only Coulomb interactions but also strong C − H⋅⋅⋅Br hydrogen-bonding forces between [MnBr₄]²⁻ and DMPBA⁺ building units. This compound exhibits a typical green emission with a high photoluminescence (PL) quantum yield value of 62.39 %. Meanwhile, [DMPBA]₂[MnBr₄] possesses a long lifetime of 1.3 ms at room temperature, which is far higher than those of reported 0D hybrid manganese bromides. Theoretical calculations show that [DMPBA]₂[MnBr₄] has a direct bandgap electronic structure with a band gap value of 2.58 eV where the valence band maximum and conduction band minimum are entirely governed by [MnBr₄]²⁻ units. As the temperature increases from 120 to 400 K, the PL emission of [DMPBA]₂[MnBr₄] presents a monotonically blue shift, which is ascribed to the decreased crystal field strength of Mn²⁺ owing to the effect of lattice thermal expansion. In addition, [DMPBA]₂[MnBr₄] exhibits a crystal-glass transition behavior and the glassy sample shows a near-yellow emission under UV light excitation.